Anticarbon device for the scroll fuel carburetor

ABSTRACT

An anticarbon device for a scroll-type carburetor consists of a frustro-conical plug mounted on the upstream wall of the spin chamber at a location along the axis of the core outlet and the primary vortex. A plurality of passageways formed therethrough permit air to be introduced into the scroll and directed against those wall locations where carbon deposits usually form because of the reverse high temperature gas flow. The plug also retains the high air/fuel velocities through the swirl vanes for flashback prevention.

United States Patent [191 Salvi ANTICARBON DEVICE FOR THE SCROLL FUELCARBURETOR [75] Inventor: Enrico Salvi, Salem, Mass.

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

[22] Filed: Mar. 15, 1973 [21] Appl. No.: 341,440

[52] Cl 60/39.74 R, 239/400, 239/404,

[51] Int. Cl. F02c 7/22 [58-] Field of Search 60/39.74 R, 39.74 B;239/400, 403-406; 261/79; 431/185, 183

[56] References Cited UNITED STATES PATENTS 3,605,405 Dubell et al.60/39.74 R

m1 3,808,803 May 7,1974

Primary Examiner-Carlton R. Croyle Assistarit ExaminerR0bert E. .GarrettAttorney, Agent, or Firm-R. S. Sciascia; L. l. Shrago 7] ABSTRACT Ananticarbon device for a scroll-type carburetor consists of afrustro-conical plug mounted on the upstream wall of the spin chamber ata location along the axis of the core outlet and the primary vortex. Aplurality of passageways formed therethrough permit air to be introducedinto the scroll and directed against those wall locations where carbondeposits usually form because of the reverse high temperature gas flow.The plug also retains the high air/fuel velocities through the swirlvaries for flashback prevention.

8 Claims, 4 Drawing Figures ANTICARBON DEVICE FOR THE SCROLL FUELCARBURETOR The present invention relates generally to scroll fuelcarburetors and, more particularly, to an anticarbon device for suchcarburetors which eliminates smoke without reducing the requiredflashback margin.

One of the proposed solutions for minimizing air pollution caused byvisible smoke emission from gas turbine engines involves carbureting theinlet air and delivering the combustible fuel/air mixture into theprimary zone of the combustor as a vortical flow. The apparatus whichachieves thi mode of operation generally comprises a housing defining aspin chamber that is centrally disposed about a core outlet. Fuel andair introduced into this chamber circulate through an array of swirlvanes and emerge as a vortical discharge flow of air and highlydispersed fuel. A skirt at the core outlet collects any non-varporizedor atomized fuel that might otheerwise be expelled from the system, anda secondary array of swirl vanes disposed about this collector developsa secondary vortical flow into the combustion chamber about the primaryvortex.

Such apparatus has been found to produce an extremely well vaporizedfuel/air mixture which may be efficiently burned in the combustionchamber with reduced smoke emission. However, under certain operatingconditions, the reduced pressure of the vortex core causes a reverse orrecirculation flow to take place from the combustion chamber back to thecentral portion of the spin chamber. Although this recirculation doescontribute to further vaporization of any liquid fuel from the spinchamber surfaces, this high temperature gas movement can haveundesirable effects on the performance of the apparatus if it is notcounteracted. For example, carbon deposits may accumulate on theupstream wall surface of the spin chamber and cause unstable burningconditions within the combustion chamber. Additionally, the hightemperature gas impinging on this upstream wall may produce prematurestructural damage.

One technique that has been proposed to avoid these conditions involvesperforating the upstream wall and sending large amounts of high velocityair ito the spin chamber to oppose the hot recirculating gases. 1 ordernot to upset the primary vortex and destroy the basic zero-dynamics ofthe system, this purge air has a swirl imparted to it that is in thesame direction as the primary vortex flow. I

It has been found that there is still a tendency for a stagnation zoneto occur at the center of the back face of the scroll. Carbon,consequently, may continue to accumulate on this portion of the upstreamwall.

With the scroll type combustors, flashback maybe experienced when thefluid velocities through the vanes are not sufficiently high. Thesevelocities have been increased by reducing the scroll-vane height. Butwhen this is done by, for example, inserting a plug at the back of thescroll, the richness of the fuel mixture in the scroll increases andproduces smoke.

It is, accordingly, a primary object of the present invention to providean anticarbon device for a scroll fuel vaporizer.

Another object of the present invention is to provide an anticarbondevice for a scroll fuel carburetor which minimizes smoking and retainshigh vane velocities for flashback prevention.

Briefly, and in somewhat general terms, the above objects areaccomplished according to the present invention by positioning a plug atthe upstream or back face of the scroll at a location which is along thecentral axis of the spin chamber so as to be co-axial with the coreoutlet and the primary vortex. This member, which has the general shapeof a frustrated cone, extends across the spin chamber and projects ashort distance into theinterior of the skirt. A plurality ofcircumferential apertures and a central aperture are provided in thecone thus permitting controllable amounts of air to be introduced intothe scroll and directed against preselected back wall areas. This airprevents the build up of carbon deposits on these surfaces and alsoleans out the very rich mixture which otherwise oc curs in this generalregion of the scroll and causes smoking.

The plug also retains the presentsmall scroll-vane height associatedwith high fluid velocities throughthe vanes. This, as is known in theart, eliminates the possibility of flashback. Additionally, the surfaceof the anticarbon device is continuously scrubbed with the fuel- /airmixture, and this constant cleaning discourages any carbon accumulationon this device.

Other objects, advantages'and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a fragmentary axial cross-sectional view of an exemplary gasturbine engine combustion apparatus which may utilize the improvedscroll. carburetor of the present invention;

FIG. 2 is a cross-sectional view of a scroll showing one modification ofthe anticarbon device mounted in place;

FIG. 3 is a front-view showing the locations of the various apertures;and

FIG. 4 schematically illustrates another configuration of the anticarbonplug.

Referring now to the drawings, FIG. 1 schematically illustrates thegeneral cooperation between a gas turbine engine and a scroll fuelcarburetor of the type which may utilize the present invention. Thedetails of this system are shown in U. S. Pat. No. 3,605,405. of Sept.20, I971 and reference may be had to this patent for a completedescription of the operation and performance of the particular scrollcarburetor shown. It

would be pointed out, however, that carburetor34 produces both a primaryvortical flow 40 and a secondary vortical flow 67. However, thesecondary flow need not be present as far as the operating principle ofthe present invention is concerned.

Referring now to FIG. 2, it will be seen that housing 35 of carburetor34 is formed by an involute outer wall 48 and a pair of planar spacedupstream and downstream end walls 50 and 52, respectively. The air/fuelmixture introduced into end opening 55 thus experiences a circularmotion of ever-decreasing radius in spin chamber 46, and, this, togetherwith the action of swirl vanes such as 31, 32 within this chamber,produces the primary vortical flow 40.

The reduced pressure condition at the vortex core 56 causes the reverseflow, previously mentioned, to be established from combustion chamber 14back into spin chamber 46, as shown by arrow 82. While thisrecirculation is beneficial in that it enhances vaporization of theliquid fuel from the spin chamber surfaces and any atomized fueldroplets carried by the air intake, it does, unfortunately, havedetrimental effects if it is allowed to impinge upon the upstream endwall 50 of the spin chamber. For example, this high temperature mayoverheat this wall surface and cause structural deformation or damage.Additionally, it may cause the accumulation of carbon deposits on theinterior wall surfaces and produces unpredictable burning conditions inthe combustion chamber 14.

To eliminate this problem, as shown in FIG. 2, an anticarbon device 80is mounted or otherwise secured to end wall 50 at a location which liesalong the central axis of the core outlet and the primary vortex. Thisapparatus has the general shape of a truncated cone with, in thisparticular case, its outer surface 51 concave.

A plurality of apertures such as 90 and 91, better shown in FIG. 3, arecut through this member at a circle of locations adjacent its rimportion. Also, a central aperture 92 of progressingly greater diameteris formed therein was to provide a circular edge 93 at the apex.

The dimensions of plug 80 are such that its conical body portion extendscompletely across the spin chamber, with its apex portion projecting ashort distance into the interior of skirt 89.

Cooperating with plug 80 is a spaced deflector 94 which has a centralopening 96 formed therein to accommodate the anticarbon plug in aconcentric manner. Deflector 94 includes a ring portion disposed withinthe spin chamber so as to confrontthe circle of air inlet apertures. Aplurality of integrally formsupporting tabs project from this ringportion and are secured to the outside surface of the back wall.Alternatively, these tabs may be directly attached near the outer rimportion of the conical plug 80 so as to permit the insertion of thecomplete apparatus, that is, the plug and the deflector into the scrollas a unitary device. In this case, any suitable mounting arrangement maybe employed to position this device in place on the back wall of thescroll.

In any event, the purpose of this deflector is to direct the air, whichis injected into the interior of the scroll via the circle of apertures,such as 90 and 91, upstream against end wall 50 of the scroll. This airflow prevents the accumulation of any carbon on the swept surroundingwall surface. Some of this air is also admitted as a film around theconcave surface of the truncated cone, and, when it leaves the apex, itdoes not interfere with the aero-dynamics of the primary vortical flow.

The circular trailing edge 93 serves as a means from which any fuel canshear off uniformly and concentrically to the scroll exit. Centralaperture 92 is included to insure that all possible stagnation zones areeliminated.

In the operation of the apertures of FIG. 2, the fuel and air mixturepasses through the various swirl vanes, such as 31 and 32, and theprimary vortical flow is established in the usual manner. The additionalair introduced through the circle of apertures in the anticarbon device,as mentioned hereinbefore, splashes onto the upstream surface of thisscroll and prevents carbon formation thereon. Some of this air is alsoadmitted as a film around the downstream surface of the truncated cone,and, when it is discharged therefrom, counteracts the recirculationflow. Further contributing to the counteraction of this flow is the airintroducedat the central opening 92.

The fuel/air mixture emanating from the swirl vanes sstrikes the concavesurface 81 of plug 80 and, thus,

this portion of the apparatus is continuously scrubbed. This constantcleaning prevents any carbon accumulation at this site.

It will also be pointed out that the additional air introduced into thissystem via the various apertures in plug 80 leans out the otherwise veryrich mixture which sometimes is present in this region and isresponsible for some of the smoking.

FIG. 4 shows an alternative anticarbon configuration. Here the surfaceis convex rather than concave and the central aperture has a constantdiameterl What is claimed is:

1. For use in a scroll-type carburetor of the type having a spin chamberthat includes spaced upstream and downstream planar walls interconnectedby an involute wall, with said downstream wall having a circular openingthat serves as a discharge exit for the vortical fuellair mixture, thecombination of,

an anticarbon member secured to said upstream wall at a locationcorresponding to the central axis of said cirular opening,

said member having a generally frustro-conical body portion whichextends across said spin chamber with the apex thereof terminating at apoint beyond said circular opening,

said member also having a plurality of passageways formed therethroughwhich permit air to be injected into said spin chamber; and means fordeflecting some of said injected air backwardly against surroundingexterior portions of said upstream wall which are adjacent saidanticarbon member. 2. In an arrangement as defined in claim I, whereinsaid anticarbon member has a central aperture formed therein whosediameter increases to a maximum at said apex, and forms a circular edgethereat. 3. In an arrangement as defined in claim 1, wherein saidfrustro-conical body portion has a convex surface. 4. For use in ascroll-type carburetor. having a spin chamber that is formed by spacedupstream and downstream planar walls that are interconnected by aninvolute wall, with a circular opening formed in said downstream wallfor discharging the vortical fuel/air mixture into the combustionchamber, the combination of,

a generally frustro-conical member secured to said upstream wall at alocation such that the longitudinal axis of symmetry of said membercoincides with the central axis of said circular opening, said memberextending across said spin chamber with the apex thereof terminating ata point beyond said circular opening,

said member also having formed therein a plurality of passageways whichpermit air to be injected from outside said spin chamber into theinterior thereof; and

means for deflecting some of said injected air against surroundingexterior portions of said upstream wall and forwardly along the surfaceof said member so as to counteract any recirculainto said spin chamber.

apex of said member. 7. In an arrangement as defined in claim 4, whereinsome of said passageways of said plurality are arranged in a circle. 8.In an arrangement as defined in claim 4,

wherein the outer surface of said member'is curyed.

1. For use in a scroll-type carburetor of the type having a spin chamberthat includes spacEd upstream and downstream planar walls interconnectedby an involute wall, with said downstream wall having a circular openingthat serves as a discharge exit for the vortical fuel/air mixture, thecombination of, an anticarbon member secured to said upstream wall at alocation corresponding to the central axis of said cirular opening, saidmember having a generally frustro-conical body portion which extendsacross said spin chamber with the apex thereof terminating at a pointbeyond said circular opening, said member also having a plurality ofpassageways formed therethrough which permit air to be injected intosaid spin chamber; and means for deflecting some of said injected airbackwardly against surrounding exterior portions of said upstream wallwhich are adjacent said anticarbon member.
 2. In an arrangement asdefined in claim 1, wherein said anticarbon member has a centralaperture formed therein whose diameter increases to a maximum at saidapex, and forms a circular edge thereat.
 3. In an arrangement as definedin claim 1, wherein said frustro-conical body portion has a convexsurface.
 4. For use in a scroll-type carburetor having a spin chamberthat is formed by spaced upstream and downstream planar walls that areinterconnected by an involute wall, with a circular opening formed insaid downstream wall for discharging the vortical fuel/air mixture intothe combustion chamber, the combination of, a generally frustro-conicalmember secured to said upstream wall at a location such that thelongitudinal axis of symmetry of said member coincides with the centralaxis of said circular opening, said member extending across said spinchamber with the apex thereof terminating at a point beyond saidcircular opening, said member also having formed therein a plurality ofpassageways which permit air to be injected from outside said spinchamber into the interior thereof; and means for deflecting some of saidinjected air against surrounding exterior portions of said upstream walland forwardly along the surface of said member so as to counteract anyrecirculation flow from said combustion chamber back into said spinchamber.
 5. In an arrangement as defined in claim 4, wherein one of saidpassageways formed in said member is located along said longitudinalaxis of symmetry.
 6. In an arrangement as defined in claim 5, whereinsaid one passageway increases in size such that the maximum openingthereof occurs at the apex of said member.
 7. In an arrangement asdefined in claim 4, wherein some of said passageways of said pluralityare arranged in a circle.
 8. In an arrangement as defined in claim 4,wherein the outer surface of said member is curved.